Riverside Research Institute and the University of Hawaii and its affiliated Kuakini Medical Center propose to investigate the use "of novel ultrasonic methods for discriminating between cancer-containing and cancer-free axillary lymph nodes of breast-cancer patients. Our emphasis will be on improving sentinel-node dissection biopsy procedures for breast-cancer patients;however, success in this project will benefit lymph- node evaluations of all types, not only for breast cancer, but also for a range of other cancers, including colorectal, epidermal (e.g., malignant melanoma), lymphatic, etc. Our premise is that the backscattering features of cancer-containing and cancer-free nodes differ sufficiently to differentiate between them using the proposed methods. Based on our extremely encouraging preliminary studies, our general hypothesis is that these methods can identify cancer-containing regions of dissected nodes using very-high-ultrasound frequencies with a simultaneous sensitivity and specificity of at least 90%. Our preliminary studies provide strong encouragement that our methods easily will validate this hypothesis. Our primary specific aims are to develop our methods when applied using very-high frequencies in the pathology laboratory to identify regions of nodes that warrant careful histologic examination. The methods we propose would be applied intra-operatively to better detect occult micrometastasis in sentinel-node dissections, and post-operatively to better detect metastasis in nodes excised by formal or radical dissections as well as in sentinel nodes. Our intention is to reduce markedly the failure of existing histopathological methods to detect metastases in 25% to 30% of excised nodes. We also aim to gain insight into underlying ultrasound-scattering mechanisms in lymph nodes. If we are successful in achieving our aims, major near-term benefits will result in evaluations of axillary lymph nodes in breast-cancer cases, and in the longer term, similar benefits will result in nodal evaluations for other cancers.